Categories and structures
A syntactic category is a group of words in a given language that can replace one another in any sentence of the language whatsover without affecting grammaticality.
A syntactic category contains single word only is called a lexical category. And if it contains sequences of words is called a nonlexical category, or a phrase category.
Condition (rule) is any sequence of English that represents the sequence of categories ART, N, V, ART, N is a grammatical sentence of English.
Phrase category is ruled by a phrase structure rule.
The phrase structure rule does not say that a grammatical sentence must look like, but it says that a grammatical sentence can look like.
There are numerous rules assigned to the phrase structure rule as like
o SNP VP
o SNP M VP
o NPART ADJ N
o NPART N
o VPVt NP
The proper use of power
A theory of grammar that says that something is possible that in fact does not occur in human language is too powerful.
If something occurs in natural language for which a theory of grammar does not permit an adequate description, then the theory is not powerful enough to capture all there is to say about language.
In fact, the deep structure only is not powerful enough to capture all there is to say about language, e.g. sentence: what will you do?
Thus, to encounter this inadequacy, there is transformation process that is ruled by transformational rule.
By the transformation rule, the deep structure becomes surface structure that is possibly more powerful than deep structure alone.
The power of transformation
It is still questionable whether transformational rule is adequately powerful, for it can possibly cover phenomena that does not occur in natural language. In other word, it can be even too powerful.
To answer the question about the adequacy of transformation, we need to investigate more about natural language occurs in rthe real life.